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Anyone have a 5/8 UNF blanking plug?

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Jimflorida

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I need a 5/8 UNF blanking plug so that I can block off the hole in the head for the water temperature sensor (I am plugging the sensor into the radiator). I see that they have a blanking plug for this purpose for sale in the UK, but can't find one any closer (can't even find a 5/8 UNF bolt anywhere locally). May just have to order from the UK, but wanted to check first if anyone has one.
Jim
 
Jim,
Try Winter Park Ace Hardware on Orange?. they have a pretty good selection of hardware.

I'd love to see how your coming, will you be finished in time for the Meade Garden show?
Phil

Also on Lee Rd is a BIG surplus harware stoe with a roketship out front. I haven't been in but I hear they have a lot of goods.
 
Jim:
That should be a 3/8" BSP (British Straight Pipe) fitting. Factory installation uses a copper sealing gasket behind the temp sensor adaptor. 5/8" UNF bolts thread in a little way and then grab. My usual fix is to use the plug from a 948/1098 head since they had that hole plugged from the factory (temp sensor in the radiator). Another remedy is to take a front crank pulley nut and cut the head (1-5/16") off. Slot the remaining threaded piece with a hacksaw on the severed end for use to screw the plug in the head. Seal the threads with teflon tape, thread sealer or RTV Ultra Grey. Thread is the same (3/8" BSP) on the water pump connection.

HTH
Mike Miller
 
Mike:
I read on some other forums that this was a 3/8 BSP fitting, and ordered one from the UK, but it does not fit. It seems to be slightly too big and does not even engage the threads. I did find at a local shop an old 1098 head with this plug installed, but it had been in there so long, it wasn't coming out.
 
Jim,

I'll double check the size at the shop tonight. (After thinking on this a while, I doubt it is 3/8" BSP like I was originally inclined. I'm thinking it is an odd-ball 5/8" thread. Like maybe -16 or -20 threads per inch. Not the same as a UNF thread.)

There are the same threaded plugs in some of the 1-1/4" and 1-1/2" intake manifolds that are the same thread. Check them out. Otherwise, send PM with address and I'll send you one ($1 plus S/H). Or, I'll be in Orlando on Major Blvd for business 1/20 - 1/23. Come by, pick it up and have a beer together. Mike
 
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Well, Bill, that is something I would never have thought about!
 
Checked the thread last night at the shop. It is 5/8"-16. OD a nominal 0.617" There are various plugs/bolts/items around and on a Spridget and other BMC products that are that thread size and pitch. Some of the plugs on the MGA and MGB intake manifolds are the 5/8"-16 thread. A 3/8"BSP has 19 threads and a nominal OD of 0.650". Too big to fit and wrong pitch.
Mike
 
Please check the threads again. The thread is 18 TPI. If you don't have a thread gauge or if the engraving on your thread gauge is hard to read, compare the threads on an old temperature sending unit to smaller bolts that you will likely have. 5/16 UNC is 18 TPI and will match the threads on the sending unit, 3/8 UNC is 16 TPI and it will not match the sender theads. If you have a 5/16-18 die (I bought one off eBay just for this sort of thing) you can re-thread a 3/8 NPT pipe plug (brass is easier to re-thread than iron or steel) to serve as a temperature sending unit plug.

The manifold threads are also 18 TPI as are the threads of the oil feed banjo bolt that goes into the block of A-series engines.
 
Thanks, Mike. If it is the same thread that is on one of the bolts on the intake manifold, I think I may have an old one around somewhere. If I can't find it, I will take you up on your kind offer to send me one.
Jim
 
Yep, normal 5/8"-18 fine, which is not hard to find, just hard to find in a bolt short enough for this use. You'll need to use a crush washer for sealing. These bolt show up in some of the Mini heads, it would be brass bolt from the factory, not that is has to be brass.


Do a google search on 5/8'-18 drain plugs you'll find several ideas, the best option looks like a drain plug used for Harley engines, the deal is it needs to be about 1/2" long and most 5/8" bolts are longer than this, normally starting at 1". I always found when all else fails just type in to Google exactly what you are looking for and you will amazed at the results. I was looking for a 7/8" bore hiem joint a few weeks ago, every one was quoting me crazy prices, well over $100, I ended Googling "7/8" bore heim joint" and found exactly what I needed, of all place, I found it at Amazon for $30. When you unsure of a bolt 's size, two things come in handy, a dial caliper to measure the diameter, and a thread gauge to determine the thread count per inch. I've also found afew times where thread were BSP, like the drain paddcok on a MGB, but inthe case of that blt the thread is almostidenticval to 1/2"-20 and tt what i used to plug those engine dran hoes ona MGB, heck thats where I mounted one of the pick up points for sdie engien stand adapter, never stripped one yet. Jim called me about this last week, and on this application, it is definately not not BSP, it for sure 5/8"- 18, I tested this for him while we were talking on the phone. I had a new 5/8'-18 bolt and test screwing into a couple of 1275 heads, it was a perfect thread match.
 
Checked the threads again. 5/8"-18 just as stated by Mssrs. Lawson and Waldrop. Batting 0-2. But, the thread on the water pump connection on the underside of the head is 5/8"-16. Put a cut off crank bolt in one the other day. At least got that one right. Oh-well.

Checked the thread pitch on a stock 1275 style temperature adapter and screwed a new 5/8"-18 Lamalloy 9 bolt into the hole in the side of a head. Same results as Hap. Threaded in just fine. Also found a brass JIC plumbing plug that fit just fine too. The plumbing plug makes a better sealing item that a bolt.

Should have checked each thread more closely - my bad. Anyway, it shouldn't be too hard to find something to plug up that hole.

Mike
 
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